Sounds like some Admin abuse that you are referring to is related to a few or a number of private PvP servers. Please be a bit more clear with that since it would scare people from playing on private servers, especially PvE servers.
I have no issue with donations granting privileges (Pippi commands) for players on a PvE server which has no effect on another player without those privileges. My servers cost currently $600 annually and getting some small donations helps keeps the costs being too high, with another server planned. I would agree if its PvP server that would not be fair.
Yes, Admin abuse ruins the fun for those want a fair game, so I agree that is one of the downfalls of a private server. There is a mod Strays No Admin which blocks admins using cheats. Not sure if this still works or not since its old. There may be another mod that does the same out there which I am not familiar with. If the mod works, it could be requested by the players to be added to the server.
There is always pros and cons to each server (Official and Private), having active admin, no admin, admin abuse, trolls/toxic community, good community, outrageous bases, etc.